Transmitter, receiver, transmission method, and reception method

ABSTRACT

Provided is a transmitter which improves the flexibility of SRS resource allocation without increasing the amount of signaling for notifying the cyclic shift amount. In the transmitter, with regard to each basic shift amount candidate group having a basic shift amount from 0 to N-1, a transmission control unit ( 206 ) specifies the actual shift amount imparted to a cyclic shift sequence used in scrambling a reference signal transmitted from each antenna port, said specification being performed based on a table in which cyclic shift amount candidates correspond to each antenna port, and based on setting information transmitted from a base station ( 100 ). With regard to basic shift amount candidates for shift amount X, the table differentiates between an offset pattern comprising offset values for cyclic shift amount candidates corresponding to each antenna port and an offset pattern corresponding to basic shift amount candidates of X+N/2.

BACKGROUND Technical Field

The present invention relates to a transmitter apparatus, a receiverapparatus, a transmission method, and a reception method.

Description of the Related Art

In 3GPP LTE (3rd Generation Partnership Project Long-term Evolution,hereinafter, simply referred to as “LTE”) and LTE-Advanced (hereinafter,simply referred to as “LTE-A”), Sounding Reference signal (SRS) is usedas a reference signal for measuring uplink receiving quality (refer toNon-Patent Literature 1). To be more specific, SRS includes P-SRS(Periodic SRS) and DA-SRS (Dynamic Aperiodic SRS). For both types ofSRS, SRS transmission timing is controlled according to triggerinformation transmitted from a base station to a terminal. However,while the P-SRS is controlled by a high-order layer, the DA-SRS iscontrolled by a control channel (that is, PDCCH) of a physical layer.

In order to transmit the SRS from a terminal to a base station, SRSresources (hereinafter, referred to as “common resources”) which arecommon to all terminals are set. A notification of these commonresources is performed with the cell units. For example, if anotification indicating that the common resources are first, third andeighth subframes is performed using control information, all terminalsin a cell stop transmission of data signals during a predetermined timeperiod (specifically, a final symbol) of each of the first, third andeighth subframes, and use the time period as a transmission resource ofa reference signal.

In addition, information regarding a resource (that is, parameters usedto identify a resource) which is practically allocated to each terminalin the common resources includes leading subframe, set band,transmission bandwidth, frame interval at which an SRS is mapped, andtransmission time or the like. Each terminal is notified of thisinformation by a higher-order layer than a physical layer.

Furthermore, SRSs are scrambled by an orthogonal sequence in eachterminal and then transmitted. Furthermore, for a terminal that performsMIMO communication introduced in LTE-A, an SRS transmitted from eachantenna port is scrambled by an orthogonal sequence and transmitted.That is, SRSs transmitted from a plurality of terminals or a terminalthat performs MIMO communication are code-division multiplexed andtransmitted.

Here, as the orthogonal sequence, a cyclic shift sequence (CS sequence)is used. More specifically, the terminal generates a transmissionsequence used by the terminal itself by applying a cyclic shiftcorresponding to one of cyclic shift amounts 0 to 7 notified of from thebase station (that is, notified by 3 bits) to a basic sequence generatedby a ZC (Zadoff Chu) sequence. To be more specific, the terminal appliesa cyclic shift to the basic sequence by a cyclic shift amount x symbollength/16 (ms) notified of from the base station. FIG. 1 shows asituation in which a basic sequence is cyclically shifted by ¼ symbol.On an LTE or LTE-A uplink, an SRS is arranged for every two subcarriers.Furthermore, on an LTE or LTE-A uplink, the same waveform is repeatedtwice within one symbol. For this reason, a waveform obtained by acyclic shift of (8 to 15)xsymbol length/16 (ms) is identical to awaveform obtained by a cyclic shift of (0 to 7)xsymbol length/16 (ms).

When SRSs are transmitted from a plurality of antennas of one terminal(that is, in a case of MIMO communication), if the base station notifiesthe terminal of cyclic shift amounts at all antennas, the signalingamount becomes enormous. Such a problem is solved by a method ofnotifying of a cyclic shift amount disclosed in, for example, Non-PatentLiterature 2. According to this method, a base station and a terminalshare an offset pattern about offset values of cyclic shift amounts of asecond antenna port, a third antenna port, and a fourth antenna portfrom the cyclic shift amount corresponding to a first antenna port(hereinafter, simply referred to as “offset pattern”). Here, the offsetpattern is fixed. In this shared condition, the base station notifiesthe terminal of the cyclic shift amount (CS0) of the first antenna portusing 3 bits. In this way, the terminal can calculate the respectivecyclic shift amounts corresponding to the second antenna port, the thirdantenna port, and the fourth antenna port from the notified cyclic shiftamount (CS0) of the first antenna port. That is, the cyclic shift amountof an i-th antenna port can be calculated from CS_(i) = CS₀ + k mod 8.Here, i is an antenna port identification number (0 to 3) and k is anoffset value of an antenna port with identification number i withrespect to the cyclic shift amount of the antenna port withidentification number 0.

FIG. 2 shows an example of correspondence table in which with regard toeight cyclic shift amount candidates of an antenna port withidentification number 0, four antenna port identification numbers areassociated with cyclic shift amounts corresponding to the respectiveantenna port identification numbers.

As is clear from FIG. 2 , in the case of 4 antenna ports (that is, thecase of 4-antenna MIMO transmission), the offset pattern is “0, 4, 2, 6”(for i=0, 1, 2, 3). On the other hand, in the case of 2 antenna ports(that is, the case of 2-antenna MIMO transmission), the offset patternis “0, 4” (for i=0, 1). Here, in FIG. 2 , antenna port 10 means a firstantenna port when one antenna port is used. Furthermore, antenna ports20 and 21 mean first and second antenna ports, respectively, when twoantenna ports are used. Furthermore, antenna ports 40, 41, 42 and 43mean first, second, third and fourth antenna ports, respectively, whenfour antenna ports are used. Using such offset patterns causes a CSinterval to become a maximum between antenna ports, and when SRSs aretransmitted from two antenna ports or when SRSs are transmitted fromfour antenna ports, the SRS demultiplexing accuracy becomes the highest.Furthermore, by causing the first two elements of the offset pattern inthe case of 4 antenna ports to match the offset pattern in the case of 2antenna ports, it is possible to use a common correspondence table forthe cases of 4 antenna ports and 2 antenna ports. A commoncorrespondence table may be used for the cases of 1 antenna port, 2antenna ports and 4 antenna ports as well.

Citation List Non-Patent Literature NPL 1

TS36.211 v8.9.0 “3GPP TSG RAN; Evolved Universal Terrestrial RadioAccess (E-UTRA); Physical Channels and Modulation”

NPL 2

R1-106007 (Mediatek Inc) Details on Aperiodic SRS

BRIEF SUMMARY Technical Problem

However, as described above, when offset pattern “0, 4, 2, 6” is used ina fixed manner, in the case of 2 antenna ports, CSs cannot be allocatedto the two antenna ports unless two CSs having a 4-CS interval arevacant, and on the other hand, in the case of 4 antenna ports, CSscannot be allocated to the four antenna ports unless four CSs having a2-CS interval are vacant. That is, there is a problem that flexibilityof resource allocation for SRSs is low. To be more specific, when 4antenna ports are used, all of cyclic shift amounts “0, 2, 4, 6” or “1,3, 5, 7” need to be unused. For example, when cyclic shift amount “0” isalready used, if cyclic shift amount “0, 2, 4, 6” is further used at 4antenna ports, cyclic shift amounts “0” are simultaneously transmittedfrom two terminals and the base station cannot demultiplex them.

It is an object of the present invention to provide a transmitterapparatus, a receiver apparatus, a transmission method, and a receptionmethod that improve flexibility of SRS resource allocation withoutincreasing an amount of signaling for notification of a cyclic shiftamount.

Solution to Problem

A transmitter apparatus according to an aspect of the present inventionis a transmitter apparatus that transmits reference signals scrambled bya cyclic shift sequence from at least some of L (L is a natural numberequal to or greater than 2) respective antenna ports, including: areceiving section that receives setting information indicating areference shift amount given to a cyclic shift sequence used to scramblea reference signal transmitted from a reference antenna port among the Lantenna ports; a specification section that specifies an amount of shiftgiven to a cyclic shift sequence used to scramble a reference signaltransmitted from each antenna port based on the setting information anda correspondence in which a cyclic shift amount candidate is associatedwith each antenna port for each of reference shift amount candidategroups having reference shift amounts 0 to N-1 (N is an even numberequal to or greater than 8); and a forming section that forms a cyclicshift sequence based on the specified amount of shift, in which in thecorrespondence, an offset pattern made up of offset values of cyclicshift amount candidates associated with each antenna port with respectto a reference shift amount candidate of reference shift amount X (X isa natural number from 0 to N/2-1 inclusive) is different from an offsetpattern made up of offset values of cyclic shift amount candidatesassociated with each antenna port with respect to a reference shiftamount candidate of reference shift amount X+N/2.

A transmitter apparatus according to another aspect of the presentinvention includes: a signal forming section that maps a referencesignal generated using information relating to a cyclic shift amount toa frequency resource corresponding to each of a plurality of antennaports determined based on a first correspondence or a secondcorrespondence; and a transmitting section that transmits the referencesignal mapped to the frequency resource corresponding to each of theplurality of antenna ports, in which the first correspondence which is acorrespondence between each of the plurality of antenna ports and thefrequency resource when the information relating to the cyclic shiftamount is X is different from the second correspondence which is acorrespondence between each of the plurality of antenna ports and thefrequency resource when the information relating to the cyclic shiftamount is X+N/2 (where X is an integer from 0 to N/2-1 inclusive, and Nis the number of candidates of the cyclic shift amount).

A receiver apparatus according to an aspect of the present invention isa receiver apparatus that receives a reference signal scrambled by acyclic shift sequence from at least some of L (L is a natural numberequal to or greater than 2) respective antenna ports, including: ageneration section that generates setting information indicating areference shift amount given to a cyclic shift sequence used to scramblea reference signal transmitted from a reference antenna port among the Lantenna ports; a transmitting section that transmits the settinginformation to a transmitter apparatus of the reference signal; and areceiving section that specifies an amount of shift given to a cyclicshift sequence used to scramble a reference signal transmitted from eachantenna port based on the setting information and a correspondence inwhich a cyclic shift amount candidate is associated with each antennaport for each of reference shift amount candidate groups havingreference shift amounts 0 to N-1 (N is an even number equal to orgreater than 8) and receives the reference signal using the specifiedamount of shift, in which in the correspondence, an offset pattern madeup of offset values of cyclic shift amount candidates associated witheach antenna port with respect to a reference shift amount candidate ofreference shift amount X (X is a natural number from 0 to N/2-1inclusive) is different from an offset pattern made up of offset valuesof cyclic shift amount candidates associated with each antenna port withrespect to a reference shift amount candidate of reference shift amountX+N/2.

A receiver apparatus according to another aspect of the presentinvention includes: a receiving section that receives a reference signalmapped to a frequency resource corresponding to each of a plurality ofantenna ports determined based on a first correspondence or a secondcorrespondence, the reference signal being generated using informationrelating to a cyclic shift amount; and a channel quality measuringsection that measures channel quality using the reference signal, inwhich the first correspondence which is a correspondence between each ofthe plurality of antenna ports and the frequency resource when theinformation relating to the cyclic shift amount is X is different fromthe second correspondence which is a correspondence between each of theplurality of antenna ports and the frequency resource when theinformation relating to the cyclic shift amount is X+N/2 (where X is aninteger from 0 to N/2-1 inclusive, and N is the number of candidates ofthe cyclic shift amount).

A transmission method according to an aspect of the present invention isa transmission method for transmitting a reference signal scrambled by acyclic shift sequence from at least some of L (L is a natural numberequal to or greater than 2) respective antenna ports, including:receiving setting information indicating a reference shift amount givento a cyclic shift sequence used to scramble a reference signaltransmitted from a reference antenna port among the L antenna ports;specifying an amount of shift given to a cyclic shift sequence used toscramble a reference signal transmitted from each antenna port based onthe setting information and a correspondence in which a cyclic shiftamount candidate is associated with each antenna port for each ofreference shift amount candidate groups having reference shift amounts 0to N-1 (N is an even number equal to or greater than 8); and forming acyclic shift sequence based on the specified amount of shift, in whichin the correspondence, an offset pattern made up of offset values ofcyclic shift amount candidates associated with each antenna port withrespect to a reference shift amount candidate of reference shift amountX (X is a natural number from 0 to N/2-1 inclusive) is different from anoffset pattern made up of offset values of cyclic shift amountcandidates associated with each antenna port with respect to a referenceshift amount candidate of reference shift amount X+N/2.

A transmission method according to another aspect of the presentinvention includes: mapping a reference signal generated usinginformation relating to a cyclic shift amount to a frequency resourcecorresponding to each of a plurality of antenna ports determined basedon a first correspondence or a second correspondence; and transmittingthe reference signal mapped to the frequency resource corresponding toeach of the plurality of antenna ports, in which the firstcorrespondence which is a correspondence between each of the pluralityof antenna ports and the frequency resource when the informationrelating to the cyclic shift amount is X is different from the secondcorrespondence which is a correspondence between each of the pluralityof antenna ports and the frequency resource when the informationrelating to the cyclic shift amount is X+N/2 (where, X is an integerfrom 0 to N/2-1 inclusive, N is the number of candidates of the cyclicshift amount).

A reception method according to an aspect of the present invention is amethod for receiving a reference signal scrambled by a cyclic shiftsequence from at least some of L (L is a natural number equal to orgreater than 2) respective antenna ports, including: transmittingsetting information indicating a reference shift amount given to acyclic shift sequence used to scramble a reference signal transmittedfrom a reference antenna port among the L antenna ports to a transmitterapparatus of the reference signal; specifying an amount of shift givento a cyclic shift sequence used to scramble a reference signaltransmitted from each antenna port based on the setting information anda correspondence in which a cyclic shift amount candidate is associatedwith each antenna port for each of reference shift amount candidategroups having reference shift amounts 0 to N-1 (N is an even numberequal to or greater than 8); and receiving the reference signal usingthe specified amount of shift, in which in the correspondence, an offsetpattern made up of offset values of cyclic shift amount candidatesassociated with each antenna port with respect to a reference shiftamount candidate of reference shift amount X (X is a natural number from0 to N/2-1 inclusive) is different from an offset pattern made up ofoffset values of cyclic shift amount candidates associated with eachantenna port with respect to a reference shift amount candidate ofreference shift amount X+N/2.

A reception method according to another aspect of the present inventionincludes: receiving a reference signal mapped to a frequency resourcecorresponding to each of a plurality of antenna ports determined basedon a first correspondence or a second correspondence, the referencesignal being generated using information relating to a cyclic shiftamount; and measuring channel quality using the reference signal, inwhich the first correspondence which is a correspondence between each ofthe plurality of antenna ports and the frequency resource when theinformation relating to the cyclic shift amount is X is different fromthe second correspondence which is a correspondence between each of theplurality of antenna ports and the frequency resource when theinformation relating to the cyclic shift amount is X+N/2 (where X is aninteger from 0 to N/2-1 inclusive, and N is the number of candidates ofthe cyclic shift amount).

Advantageous Effects of Invention

According to the present invention, it is possible to provide atransmitter apparatus, a receiver apparatus, a transmission method, anda reception method that improves flexibility of SRS resource allocationwithout increasing an amount of signaling for notification of a cyclicshift amount.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a diagram illustrating a situation in which a basic sequenceis cyclically shifted by a ¼ symbol;

FIG. 2 is a diagram illustrating an example of a correspondence table inwhich with regard to eight cyclic shift amount candidates for an antennaport with identification number 0, four antenna port identificationnumbers are associated with cyclic shift amounts corresponding to therespective antenna port identification numbers;

FIG. 3 is a principal configuration diagram of a base station accordingto Embodiment 1 of the present invention;

FIG. 4 is a principal configuration diagram of a terminal according toEmbodiment 1 of the present invention;

FIG. 5 is a block diagram illustrating a configuration of the basestation according to Embodiment 1 of the present invention;

FIG. 6 is a block diagram illustrating a configuration of the terminalaccording to Embodiment 1 of the present invention;

FIG. 7 is a diagram illustrating a code resource setting rule tableaccording to Embodiment 1 of the present invention;

FIG. 8 is a diagram illustrating a code resource setting rule tableaccording to Embodiment 2 of the present invention;

FIG. 9 is a diagram illustrating inter-sequence interference;

FIG. 10 is a diagram illustrating an effect of using the code resourcesetting rule table in FIG. 8 ;

FIG. 11 is a diagram illustrating another code resource setting ruletable according to Embodiment 2 of the present invention;

FIG. 12 is a diagram illustrating a code resource setting rule tableaccording to Embodiment 3 of the present invention;

FIG. 13 is a diagram illustrating another code resource setting ruletable according to Embodiment 3 of the present invention;

FIG. 14 is a diagram illustrating a code resource setting rule tableaccording to Embodiment 4 of the present invention;

FIG. 15 is a diagram illustrating a case where an offset pattern appliedto 2-antenna port transmission is assumed to be “0, 4”;

FIG. 16 is a diagram illustrating a code resource setting rule tableaccording to Embodiment 5 of the present invention;

FIG. 17 is a diagram illustrating a code resource setting rule tableaccording to Embodiment 6 of the present invention;

FIG. 18 is a diagram illustrating a code resource setting rule tableaccording to Embodiment 7 of the present invention;

FIG. 19 is a diagram illustrating a problem with the conventionalcorrespondence table shown in FIG. 2 ;

FIG. 20 is a diagram illustrating a code frequency resource setting ruletable according to Embodiment 8 of the present invention; and

FIG. 21 is a diagram illustrating another code frequency resourcesetting rule table according to Embodiment 8 of the present invention.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings. In addition, in theembodiments, the same constituent elements are given the same referencenumerals, and repeated description thereof will be omitted.

Embodiment 1 Overview of Communication System

A communication system according to Embodiment 1 of the presentinvention includes base station 100 and terminal 200. Base station 100is an LTE-A base station, and terminal 200 is an LTE-A terminal.Furthermore, terminal 200 transmits a reference signal scrambled by acyclic shift sequence obtained by applying a cyclic shift to a basicsequence from at least some of L (L is a natural number equal to orgreater than 2) antenna ports. Base station 100 then receives thereference signal scrambled by a cyclic shift sequence obtained byapplying a cyclic shift to a basic sequence from at least some of L (Lis a natural number equal to or greater than 2) antenna ports.

FIG. 3 is a principal configuration diagram of base station 100according to Embodiment 1 of the present invention. In base station 100,setting section 101 generates setting information relating to areference shift amount given to a cyclic shift sequence used to scramblea reference signal transmitted from a reference antenna port among L (Lis a natural number equal to or greater than 2) antenna ports. Thegenerated setting information is transmitted to terminal 200 viatransmission processing section 104. Furthermore, reception processingsection 108 specifies an actual shift amount given to a cyclic shiftsequence used to scramble a reference signal transmitted from eachantenna port and receives the reference signal using the specifiedactual shift amount based on a correspondence in which a cyclic shiftamount candidate is associated with each antenna port and settinginformation for each of reference shift amount candidate groups havingshift amounts 0 to N-1 (N is an even number equal to or greater than 8)that a reference shift amount can take. In the above-describedcorrespondence, an offset pattern made up of offset values of cyclicshift amount candidates associated with each antenna port with respectto a reference shift amount candidate of shift amount X (X is a naturalnumber from 0 to N/2-1 inclusive) is different from an offset patternmade up of offset values of cyclic shift amount candidates associatedwith each antenna port with respect to a reference shift amountcandidate of X+N/2.

FIG. 4 is a principal configuration diagram of terminal 200 according toEmbodiment 1 of the present invention. In terminal 200, receptionprocessing section 203 receives setting information relating to areference shift amount given to a cyclic shift sequence used to scramblea reference signal transmitted from a reference antenna port among the Lantenna ports. Transmission control section 206 specifies an actualshift amount given to a cyclic shift sequence used to scramble areference signal transmitted from each antenna port based on acorrespondence in which a cyclic shift amount candidate is associatedwith each antenna port and the setting information for each of referenceshift amount candidate groups having shift amounts 0 to N-1 (N is aneven number equal to or greater than 8) that a reference shift amountcan take. In the above-described correspondence, an offset pattern madeup of offset values of cyclic shift amount candidates associated witheach antenna port with respect to a reference shift amount candidate ofshift amount X (X is a natural number from 0 to N/2-1 inclusive) isdifferent from an offset pattern made up of offset values of cyclicshift amount candidates associated with each antenna port with respectto a reference shift amount candidate of X+N/2. Transmission signalforming section 207 then maps a reference signal multiplied by thecyclic shift sequence formed based on the specified actual shift amount.

Configuration of Base Station 100

FIG. 5 is a block diagram illustrating a configuration of base station100 according to Embodiment 1 of the present invention. In FIG. 5 , basestation 100 includes setting section 101, coding/modulation sections 102and 103, transmission processing section 104, transmitting section 105,antenna 106, receiving section 107, reception processing section 108,data receiving section 109, and receiving quality measuring section 110.

Setting section 101 generates “candidate resources setting information”for setting a “candidate resource” of setting target terminal 200. Thiscandidate resource is a resource to which setting target terminal 200can map an SRS. The candidate resource setting information can bedivided into “time/frequency resource setting information” and “coderesource setting information.” The time/frequency resource settinginformation includes a leading subframe and a leading frequency band atwhich setting target terminal 200 starts to set a candidate resource anda frequency bandwidth or the like available to setting target terminal200. Furthermore, the code resource setting information includes“information relating to a cyclic shift amount” or the like. Here, the“information relating to a cyclic shift amount” is information relatingto a shift amount of a cyclic shift sequence used for SRSs transmittedfrom a reference antenna port which serves as a reference. Here,particularly, a cyclic shift amount regarding an antenna port whoseantenna port identification information is zero is used as the“information relating to a cyclic shift amount.”

When the SRS that setting target terminal 200 is instructed to transmitis a DA-SRS in particular, setting section 101 generates triggerinformation for instructing terminal 200 to start transmission of aDA-SRS. When the SRS is a P-SRS, information relating to a trigger tostart transmission of a P-SRS is included in, for example,time/frequency resource setting information.

As described above, the candidate resource setting information generatedby setting section 101 is transmitted as setting information to settingtarget terminal 200 via coding/modulation section 102, transmissionprocessing section 104, and transmitting section 105. Furthermore, thetrigger information is likewise transmitted to setting target terminal200 via coding/modulation section 102, transmission processing section104, and transmitting section 105. Furthermore, the setting informationand the trigger information are also outputted to reception processingsection 108.

In addition, setting section 101 generates allocation controlinformation which includes resource (RB) allocation information and MCSinformation regarding one or a plurality of transport blocks (TB). Theallocation control information is constituted by allocation controlinformation regarding an uplink resource (for example, PUSCH (PhysicalUplink Shared Channel)) for allocating uplink data, and allocationcontrol information regarding a downlink resource (for example, PDSCH(Physical Downlink Shared Channel)) for allocating downlink data. Inaddition, the allocation control information regarding the uplinkresource is outputted to coding/modulation section 102 and receptionprocessing section 108, and the allocation control information regardingthe downlink resource is outputted to coding/modulation section 102 andtransmission processing section 104.

Here, a notification of the setting information is sent from basestation 100 to terminal 200 as high-order layer information (that is,through RRC signaling). On the other hand, a notification of theallocation control information and the trigger information is sent frombase station 100 to terminal 200 using PDCCH (Physical Downlink ControlChannel). In other words, while the setting information has a relativelylong notification interval (that is, the notification is performed at arelatively long interval), the allocation control information and thetrigger information have a short notification interval (that is, thenotification is performed at a short interval).

Coding/modulation section 102 codes and modulates the settinginformation, the trigger information, and the allocation controlinformation received from setting section 101, and outputs the obtainedmodulation signal to transmission processing section 104.

Coding/modulation section 103 codes and modulates an input data signal,and outputs the obtained modulation signal to transmission processingsection 104.

Transmission processing section 104 maps the modulation signals receivedfrom coding/modulation section 102 and coding/modulation section 103 toa resource indicated by the downlink resource allocation informationreceived from setting section 101, thereby forming a transmissionsignal. Here, in a case where the transmission signal is an OFDM signal,the modulation signals are mapped to a resource indicated by thedownlink resource allocation information received from setting section101, are transformed into a time waveform through an inverse fastFourier transform (IFFT) process, and have CP (Cyclic Prefix) addedthereto, thereby forming an OFDM signal.

Transmitting section 105 performs wireless processes (up-conversion,digital-analog (D/A) conversion, and the like) on the transmissionsignal received from transmission processing section 104, and transmitsa resultant signal via antenna 106.

Receiving section 107 performs wireless processes (down-conversion,analog-digital (A/D) conversion, and the like) on a wireless signalreceived via antenna 106, and outputs the obtained received signal toreception processing section 108.

Reception processing section 108 specifies a resource to which theuplink data signal and ACK/NACK information are mapped based on theuplink resource allocation information received from setting section101, and extracts a signal component mapped to the specified resourcefrom the received signal.

In addition, reception processing section 108 specifies a resource towhich the SRS is mapped based on the setting information and the triggerinformation received from setting section 101.

To be more specific, reception processing section 108 specifies atime/frequency resource to which the SRS is mapped based on the“time/frequency resource setting information” and the triggerinformation. Furthermore, reception processing section 108 specifies acode resource to which the SRS is mapped (that is, cyclic shift amountof a cyclic shift sequence used to transmit the SRS) based on the “coderesource setting information” and the “code resource setting ruletable.”

Reception processing section 108 then generates a plurality of cyclicshift sequences (that is, cyclic shift sequence set) corresponding tothe plurality of specified cyclic shift amounts. Reception processingsection 108 then extracts a signal component mapped to the specifiedtime/frequency resource from the received signal and demultiplexes theplurality of code-multiplexed SRSs using the generated cyclic shiftsequence set.

Here, in a case where the received signal is a spatially multiplexedsignal (that is, transmitted using a plurality of code words (CWs)),reception processing section 108 demultiplexes the received signal foreach CW. In addition, in a case where the received signal is an OFDMsignal, reception processing section 108 transforms the received signalinto a time domain signal by performing an IDFT (Inverse DiscreteFourier Transform) process on the extracted signal component.

The uplink data signal and the ACK/NACK information extracted byreception processing section 108 in this way are outputted to datareceiving section 109, and the SRS is outputted to receiving qualitymeasuring section 110.

Data receiving section 109 decodes the signal received from receptionprocessing section 108. Thereby, the uplink data and the ACK/NACKinformation are obtained.

Receiving quality measuring section 110 measures receiving quality ofeach frequency resource unit on the basis of the SRS received fromreception processing section 108, and outputs receiving qualityinformation.

In addition, a notification of the setting information (the candidateresource setting information and the transmission method settinginformation) is preferably performed using high-order layer informationin which a notification interval is long from the viewpoint of signalingin a case where traffic circumstances do not vary in a cell of basestation 100 or average receiving quality is desired to be measured. Inaddition, a notification of a portion or all of these various offsetamounts is performed as broadcast information, thereby further reducinga notification amount. However, in a case where the setting informationis required to be more dynamically changed depending on trafficcircumstances or the like, a notification of a portion or all of theseoffset amounts is preferably performed using PDCCH in which anotification interval is short.

Configuration of Terminal 200

FIG. 6 is a block diagram illustrating a configuration of terminal 200according to Embodiment 1 of the present invention. Here, terminal 200is an LTE-A terminal.

In FIG. 6 , terminal 200 includes antenna 201, receiving section 202,reception processing section 203, reference signal generation section204, data signal generation section 205, transmission control section206, transmission signal forming section 207, and transmitting section208

Receiving section 202 performs wireless processes (down-conversion,analog-digital (A/D) conversion, and the like) on a wireless signalreceived via antenna 201, and outputs the obtained received signal toreception processing section 203.

Reception processing section 203 extracts the setting information, theallocation control information, the trigger information, and the datasignal included in the received signal. Reception processing section 203outputs the setting information, the allocation control information, andthe trigger information to transmission control section 206. Inaddition, reception processing section 203 performs an error detectionprocess on the extracted data signal, and outputs ACK/NACK informationcorresponding to the error detection result to data signal generationsection 205.

When a generation instruction signal is received from transmissioncontrol section 206, reference signal generation section 204 generates areference signal which is outputted to transmission signal formingsection 207.

Data signal generation section 205 receives the ACK/NACK information andtransmission data, and codes and modulates the ACK/NACK information andthe transmission data on the basis of MCS information received fromtransmission control section 206, thereby generating a data signal. In acase of Non-MIMO transmission, a data signal is generated using a singlecode word (CW), and, in a case of MIMO transmission, a data signal isgenerated using two (or a plurality of) code words. In addition, in acase where the received signal is an OFDM signal, data signal generationsection 205 also performs a CP removal process and an FFT process.

Transmission control section 206 sets a candidate resource to which itsown terminal maps the SRS. To be more specific, transmission controlsection 206 specifies a candidate time/frequency resource on the basisof the setting information (the time/frequency resource settinginformation) received from reception processing section 203.Furthermore, transmission control section 206 specifies a candidate coderesource (that is, cyclic shift amount of a cyclic shift sequence usedto transmit the SRS) based on the setting information (code resourcesetting information) received from reception processing section 203 andthe “code resource setting rule table.” When the trigger information isreceived from reception processing section 203, transmission controlsection 206 outputs information relating to a cyclic shift amount of acyclic shift sequence used to transmit the SRS to transmission signalforming section 207. The candidate code resource set in terminal 200will be described in detail later.

In addition, when the trigger information is received from receptionprocessing section 203, transmission control section 206 determines an“RS mapping resource” to which the SRS is practically mapped in thecandidate time/frequency resource, outputs information (hereinafter,also referred to as “RS mapping resource information”) regarding thedetermined RS mapping resource to transmission signal forming section207, and also outputs a generation instruction signal of a referencesignal to reference signal generation section 204.

In addition, transmission control section 206 specifies a “data mappingresource” to which the data signal is mapped on the basis of theallocation control information received from reception processingsection 203, outputs information (hereinafter, referred to as “datamapping resource information”) regarding the data mapping resource totransmission signal forming section 207, and also outputs the MCSinformation included in the allocation control information to datasignal generation section 205.

Transmission signal forming section 207 maps the SRS received fromreference signal generation section 204 to an RS mapping resourceindicated by the RS mapping information. Transmission signal formingsection 207 then applies a cyclic shift corresponding to informationregarding the cyclic shift amount received from transmission controlsection 206 to a reference sequence, thereby generates a cyclic shiftsequence set, and multiplies the SRS mapped to the RS mapping resourceby the cyclic shift sequence set. The SRSs multiplied by the pluralityof respective cyclic shift sequences constituting the cyclic shiftsequence set are transmitted from the corresponding antenna ports. Theplurality of SRSs are code-multiplexed in this way.

In addition, transmission signal forming section 207 maps the datasignal received from data signal generation section 205 to a datamapping resource indicated by the data mapping resource information. Inthis way, a transmission signal is formed. In addition, in a case ofNon-MIMO transmission, a data signal of one code word is allocated toone layer, and, in a case of MIMO transmission, a data signal of two (ora plurality of) code words is allocated to a plurality of layers.Further, in a case where the transmission signal is an OFDM signal,transmission signal forming section 207 performs a DFT (Discrete FourierTransform) process on the data signal which is then mapped to the datamapping resource. In addition, CP is added to the formed transmissionsignal.

Transmitting section 208 performs wireless processes (up-conversion,digital-analog (D/A) conversion, and the like) on the transmissionsignal formed by transmission signal forming section 207, and transmitsa resultant signal via antenna 201.

[Operations of base station 100 and terminal 200] Operations of basestation 100 and terminal 200 having the above-described configurationswill be described. Here, particularly, a candidate code resource settingprocess for setting target terminal 200, a transmission process of anSRS using the candidate code resource by terminal 200, and a receptionprocess of the SRS transmitted from terminal 200 by base station 100will be described. Furthermore, particularly, a case will be describedwhere terminal 200 transmits SRSs using two antenna ports or fourantenna ports.

Candidate Code Resource Setting Process for Setting Target Terminal 200

Setting section 101 generates candidate code resource settinginformation for setting a candidate code resource for setting targetterminal 200. To be more specific, setting section 101 generatesinformation relating to a shift amount of a cyclic shift sequence usedfor an SRS transmitted from the reference antenna port of setting targetterminal 200. Here, particularly, the cyclic shift amount regarding anantenna port whose antenna port identification information is zero isused as information relating to the cyclic shift amount.

The candidate code resource setting information generated in this way istransmitted to terminal 200.

SRS Transmission Process Using Candidate Code Resource by Terminal 200

Transmission control section 206 sets a candidate code resource to whichits own terminal maps the SRS. To be more specific, transmission controlsection 206 specifies a candidate code resource (that is, cyclic shiftamount of a cyclic shift sequence used to transmit the SRS) based on thecode resource setting information received from reception processingsection 203 and a code resource setting rule table.

FIG. 7 is a diagram illustrating a code resource setting rule tableaccording to Embodiment 1 of the present invention. In the code resourcesetting rule table, for each of a plurality of cyclic shift amountcandidates of the reference antenna port, four antenna portidentification numbers are associated with cyclic shift amountscorresponding to the respective antenna port identification numbers. Thenumber of cyclic shift amount candidates is 8 from 0 to 7. As describedabove, the reference antenna port is an antenna port with identificationnumber 0. In FIG. 7 , basic offset pattern “0, 4, 2, 6” is applied tocyclic shift amount candidates 0 to 3 of the antenna port withidentification number 0, whereas an offset pattern different from thebasic offset pattern is applied to cyclic shift amount candidates 4 to 7of the antenna port with identification number 0. That is, ingeneralized expression, different offset patterns are applied to cyclicshift amount candidate X and cyclic shift amount candidate X+4 of theantenna port with identification number 0. Particularly, the basicoffset pattern is applied to cyclic shift amount candidate X. Here, X isan integer from 0 to 3 inclusive.

In further generalized expression, when the number of the plurality ofcyclic shift amount candidates of the reference antenna port is assumedto be N (N is equal to or greater than 8 and power of 2), differentoffset patterns are applied to cyclic shift amount candidate X andcyclic shift amount candidate X+N/2. Here, X is an integer from 0 to(N/2-1) inclusive. Alternatively, X may be (X-N/2) mod N.

The flexibility of SRS resource allocation can be improved by using sucha code resource setting rule table including a plurality of offsetpatterns. Furthermore, by sharing the code resource setting rule tablebetween base station 100 and terminal 200 beforehand, base station 100needs only to transmit information relating to the cyclic shift amountcorresponding to the reference antenna port to terminal 200, and canthereby prevent the amount of signaling from increasing.

To be more specific, 2-antenna-port transmission allows all shift amountpairs “0, 4,” “1, 5,” “2, 6” and “3, 7” made up of two cyclic shiftamounts to be used and 4-antenna-port transmission allows both shiftamount groups “0, 2, 4, 6” and “1, 3, 5, 7” made up of four cyclic shiftamounts to be used. Thus, it is possible to secure the flexibility ofSRS resource allocation equivalent to that when the correspondence tableshown in FIG. 2 is used. For example, when terminal 1 uses “0, 4” andterminal 2 uses “1,” in the table in FIG. 2 , terminal 3 has no choicebut to select “3, 7” or “2, 6,” whereas in the table in FIG. 7 ,terminal 3 has choice to select “3, 7”, “2, 6” or “5, 6.”

Transmission signal forming section 207 then applies a cyclic shiftcorresponding to information relating to the cyclic shift amountreceived from transmission control section 206 to the referencesequence, and thereby generates a cyclic shift sequence set andmultiplies an SRS mapped to the RS mapping resource by the cyclic shiftsequence set. The SRSs multiplied by the plurality of respective cyclicshift sequences that constitute the cyclic shift sequence set aretransmitted from the corresponding antenna ports. In this way, theplurality of SRSs are code-multiplexed.

Reception Process of SRS Transmitted From Terminal 200 by Base Station100

Reception processing section 108 specifies a code resource to which anSRS is mapped (that is, cyclic shift amount of a cyclic shift sequenceused to transmit the SRS) based on the “code resource settinginformation” and the “code resource setting rule table.” The “coderesource setting rule table” used here is the same as that used interminal 200.

Reception processing section 108 generates a plurality of cyclic shiftsequences (that is, a cyclic shift sequence set) corresponding to theplurality of respective specified cyclic shift amounts. Receptionprocessing section 108 extracts a signal component mapped to thespecified time/frequency resource from the received signal anddemultiplexes a plurality of code-multiplexed SRSs using the generatedcyclic shift sequence set.

As described above, according to the present embodiment, in terminal200, reception processing section 203 receives setting informationrelating to a reference shift amount given to a cyclic shift sequenceused to scramble a reference signal transmitted from a reference antennaport among L antenna ports. Transmission control section 206 specifiesan actual shift amount given to the cyclic shift sequence used toscramble the reference signal transmitted from each antenna port basedon the code resource setting rule table in which a cyclic shift amountcandidate is associated with each antenna port and the settinginformation, regarding each of reference shift amount candidate groupshaving shift amounts 0 to N-1 (N is an even number equal to or greaterthan 8) that the reference shift amount can take. In the above-describedcode resource setting rule table, an offset pattern made up of offsetvalues of cyclic shift amount candidates associated with each antennaport with respect to a reference shift amount candidate having shiftamount X (X is a natural number from 0 to N/2-1 inclusive) is differentfrom an offset pattern made up of offset values of cyclic shift amountcandidates associated with each antenna port with respect to a referenceshift amount candidate having X+N/2. Transmission signal forming section207 forms a cyclic shift sequence based on the specified actual shiftamount.

In base station 100, setting section 101 generates setting informationrelating to a reference shift amount given to a cyclic shift sequenceused to scramble a reference signal transmitted from a reference antennaport among L (L is a natural number equal to or greater than 2) antennaports. The generated setting information is transmitted to terminal 200via transmission processing section 104. Furthermore, receptionprocessing section 108 specifies an actual shift amount given to acyclic shift sequence used to scramble a reference signal transmittedfrom each antenna port based on the code resource setting rule table inwhich a cyclic shift amount candidate is associated with each antennaport and setting information for each of reference shift amountcandidate groups having shift amounts 0 to N-1 (N is an even numberequal to or greater than 8) that the reference shift amount can take,and receives the reference signal using the specified actual shiftamount. In the above-described code resource setting rule table, anoffset pattern made up of offset values of cyclic shift amountcandidates associated with each antenna port with respect to a referenceshift amount candidate having shift amount X (X is a natural number from0 to N/2-1 inclusive) is different from an offset pattern made up ofoffset values of cyclic shift amount candidates associated with eachantenna port corresponding to a reference shift amount candidate ofX+N/2.

Embodiment 2

Embodiment 2 relates to a variation of the “code resource setting ruletable.”

FIG. 8 is a diagram illustrating a code resource setting rule tableaccording to Embodiment 2 of the present invention.

In FIG. 8 , basic offset pattern “0, 4, 2, 6” is applied to cyclic shiftamount candidates 0 to 3 of an antenna port with identification number0, whereas an offset pattern different from the basic offset pattern isapplied to cyclic shift amount candidates 4 to 7 of the antenna portwith identification number 0. That is, in generalized expression,different offset patterns are applied to cyclic shift amount candidate Xand cyclic shift amount candidate X+4 of the antenna port withidentification number 0. In particular, the basic offset pattern isapplied to cyclic shift amount candidate X, whereas offset pattern “0,1, 2, 3” or “0, -1, -2, -3” is applied to cyclic shift amount candidateX+4. Here, X is an integer from 0 to 3 inclusive.

That is, by using offset pattern “0, 1, 2, 3” or “0, -1, -2, -3,” thefour cyclic shift amounts that constitute the cyclic shift amount sethave continuous values.

Furthermore, in FIG. 8 , regarding cyclic shift amount candidate X+4 towhich an offset pattern other than the basic offset pattern is applied,one of “0, 1, 2, 3” and “0, -1, -2, -3” is applied when X+4 is an evennumber, and the other is applied when X+4 is an odd number.

When a plurality of terminals 200 transmit SRSs, the number of locationswhere inter-sequence interference occurs increases depending ondifferences in transmission timing among terminals. For example, whenterminal 200-1 uses shift amount group “0, 4, 2, 6” and terminal 200-2uses shift amount group “1, 5, 3, 7,” if transmission timing of terminal200-2 is shifted, inter-sequence interference is given to a cyclic shiftsequence of all cyclic shift amounts “0, 4, 2, 6” of terminal 200-1(refer to FIG. 9 ).

In contrast, as described above, regarding cyclic shift amount candidateX+4, one of “0, 1, 2, 3” and “0, -1, -2, -3” is applied when X+4 is aneven number, and the other is applied when X+4 is an odd number, and inthis way even when transmission timing is shifted, it is possible toreduce the number of locations where inter-sequence interference occurs.For example, when terminal 200-1 uses shift amount group “4, 5, 6, 7”and terminal 200-2 uses shift amount group “0, 1, 2, 3,” even iftransmission timing of terminal 200-2 is shifted, inter-sequenceinterference occurs at only one location of cyclic shift amount “4” ofterminal 200-2 (refer to FIG. 10 ).

If components of a shift amount group are continuous, which antenna portshould be associated with each component is not particularly limited.For example, as shown in FIG. 11 , even if the cyclic shift amounts usedby the antenna port with identification number 1 and the antenna portwith identification number 2 are discontinuous, there will be no problemif components of the shift amount group are continuous. In this way, itis possible to create a code resource setting rule table with less biasin the cyclic shift amount used for SRSs.

Embodiment 3

Embodiment 3 relates to a variation of the “code resource setting ruletable.”

FIG. 12 is a diagram illustrating a code resource setting rule tableaccording to Embodiment 3 of the present invention.

In Embodiment 3 as in the case of other embodiments, different offsetpatterns are applied to cyclic shift amount candidate X and cyclic shiftamount candidate X+4 of the antenna port with identification number 0.Furthermore, in Embodiment 3, different offset patterns are applied tocyclic shift amount candidate 2 M (M=0, 1, ...) and cyclic shift amountcandidate 2 M+1. While a basic offset pattern is applied to one ofcyclic shift amount candidate 2 M and cyclic shift amount candidate 2M+1, offset pattern “0, 1, 2, 3” or “0, -1, -2, -3” is applied to theother (refer to FIG. 12 ).

Here, in the code resource setting rule table shown in FIG. 11 , whenattention is focused on a cyclic shift amount group to which an offsetpattern other than the basic offset pattern is applied, the cyclic shiftamount pairs corresponding to identification numbers 0 and 1 used for2-antenna transmission are limited to “4, 3” “5, 6,” “6, 5” and “7, 0”and no pair exists for cyclic shift amounts 1 and 2. That is, cyclicshift amounts 1 and 2 cannot be allocated.

In contrast, as shown in FIG. 12 , while the basic offset pattern isapplied to one of cyclic shift amount candidate 2 M and cyclic shiftamount candidate 2 M+1, offset pattern “0, 1, 2, 3” or “0, -1, -2, -3”is applied to the other, and it is thereby possible to reduce the biasin the cyclic shift amount applied to the antenna port withidentification number 1. To be more specific, in FIG. 12 , whenattention is focused on the cyclic shift amount group to which an offsetpattern other than the basic offset pattern is applied, the cyclic shiftamount pairs corresponding to identification numbers 0 and 1 used for2-antenna transmission are “4, 5”, “1, 0,” “6, 7” and “3, 2” and thecyclic shift amount is more distributed, with less bias.

Based on the code resource setting rule table shown in FIG. 11 , FIG. 12shows a code resource setting rule table obtained by applying differentoffset patterns to cyclic shift amount candidate 2 M (M=0,1, ...) andcyclic shift amount candidate 2 M+1 as an example. That is, in coderesource setting rule tables other than that in FIG. 11 shown in thepresent specification, different offset patterns may be applied tocyclic shift amount candidate 2 M (M=0,1, ...) and cyclic shift amountcandidate 2 M+1.

Furthermore, when different offset patterns are applied to cyclic shiftamount candidate 2 M (M=0,1, ...) and cyclic shift amount candidate 2M+1, if there are two continuous cyclic offset amount candidates amongcyclic shift amount candidates of the reference antenna port which areassociated with offset patterns other than the basic offset pattern,offset pattern “0, 1, 2, 3” may be associated with one (for example, onewith a smaller value), and offset pattern “0, -1, -2, -3” may beassociated with the other (for example, one with a greater value). InFIG. 13 , while offset pattern “0, 1, 2, 3” is associated with cyclicshift amount 3 of the antenna port with identification number 0, offsetpattern “0, -1, -2, -3” is associated with cyclic shift amount 4 of theantenna port with identification number 0.

This makes it possible to cause the cyclic shift amount to bedistributed in both cases of 2-port antenna transmission and 4-portantenna transmission, thus preventing bias. As a result, the flexibilityof SRS resource allocation can be improved.

Embodiment 4

Embodiment 4 relates to a variation in the “code resource setting ruletable.”

FIG. 14 is a diagram illustrating a code resource setting rule tableaccording to Embodiment 4 of the present invention.

In FIG. 14 , while basic offset pattern “0, 4, 2, 6” is applied tocyclic shift amount candidates 0 to 3 of an antenna port withidentification number 0, an offset pattern different from the basicoffset pattern is applied to cyclic shift amount candidates 4 to 7 ofthe antenna port with identification number 0. That is, in generalizedexpression, different offset patterns are applied to cyclic shift amountcandidate X and cyclic shift amount candidate X+4 of the antenna portwith identification number 0. In particular, while the basic offsetpattern is applied to cyclic shift amount candidate X, offset pattern“0, 4, 1, 5” or offset pattern “0, 4, 3, 7” is applied to cyclic shiftamount candidate X+4. That is, with the offset pattern group applied tocyclic shift amount candidates 4 to 7 of the antenna port withidentification number 0, all offset patterns are common in that thedifference in the cyclic shift amount applied to the antenna port withidentification number 0 and the antenna port with identification number1, and the difference in the cyclic shift amount applied to the antennaport with identification number 2 and the antenna port withidentification number 3 are 4. In contrast, with the offset patterngroup applied to cyclic shift amount candidates 4 to 7 of the antennaport with identification number 0, there are a plurality of values inthe difference in the cyclic shift amount applied to the antenna portwith identification number 1 and the antenna port with identificationnumber 2.

Here, 2-antenna port transmission is more likely to be applied toterminal 200 than 4-antenna port transmission. As shown in FIG. 15 , ifan offset pattern applied to 2-antenna port transmission is assumed tobe “0, 4,” cyclic shift amount pairs “0, 4”, “2, 6,” “1, 5” and “3, 7”are used for terminals 200-1 to 4, respectively, (denoted by UEs #1 to 4in FIG. 15 ).

In this state, two terminals 200 are assumed to end SRS transmission.For example, when UE#1 and UE#2 end SRS transmission, cyclic shiftamount set “0, 4, 2, 6” becomes vacant. Furthermore, when UE#1 and UE#3end SRS transmission, cyclic shift amount set “0, 4, 1, 5” becomesvacant. Furthermore, when UE#1 and UE#4 end SRS transmission, cyclicshift amount set “0, 4, 3, 7” becomes vacant. Furthermore, when UE#2 andUE#4 end SRS transmission, cyclic shift amount set “2, 6, 3, 7” becomesvacant. Furthermore, when UE#3 and UE#4 end SRS transmission, cyclicshift amount set “1, 5, 3, 7” becomes vacant. Assuming that SRSs of 4antenna ports are flexibly allocated to these vacant CSs, offset amountsets “0, 4, 2, 6,” “0, 4, 1, 5” and “0, 4, 3, 7” are effective.

Therefore, while the basic offset pattern is applied to cyclic shiftamount candidate X, offset pattern “0, 4, 1, 5” or offset pattern “0, 4,3, 7” is applied to cyclic shift amount candidate X+4. Thereby, even iftwo vacant CSs with a 4-CS interval exist, it is possible to make SRSresource allocation easier in 4-antenna port transmission. For example,even if vacant CSs are “0, 4, 1, 5,” SRS resources for 4-antenna porttransmission can be allocated.

Embodiment 5

Embodiment 5 relates to a variation in the “code resource setting ruletable.”

FIG. 16 is a diagram illustrating a code resource setting rule tableaccording to Embodiment 5 of the present invention.

In FIG. 16 , while basic offset pattern “0, 4, 2, 6” is applied tocyclic shift amount candidates 0 to 3 of an antenna port withidentification number 0, an offset pattern different from the basicoffset pattern is applied to cyclic shift amount candidates 4 to 7 ofthe antenna port with identification number 0. That is, in generalizedexpression, different offset patterns are applied to cyclic shift amountcandidate X and cyclic shift amount candidate X+4 of the antenna portwith identification number 0. In particular, while a basic offsetpattern is applied to cyclic shift amount candidate X, offset pattern“0, 3, A, B” or “0, 5, A, B” is applied to cyclic shift amount candidateX+4. Here, A and B are different values. Furthermore, A and B arenatural numbers other than 0 and 3 among 0 to 7 in a case of offsetpattern “0, 3, A, B” and natural numbers other than 0 and 5 among 0 to 7in a case of offset pattern “0, 5, A, B.”

Here, in Embodiment 4, in order for the receiving side to demultiplexSRSs with high accuracy in a case of 2-antenna port transmission, thedifference in applied cyclic shift amount between the antenna port withidentification number 0 and the antenna port with identification number1 is designed to be 4. However, when emphasis is placed on theflexibility of SRS resource allocation in a case of 2-antenna porttransmission, it is preferable to provide a plurality of differencevalues in the applied cyclic shift amount between the antenna port withidentification number 0 and the antenna port with identificationnumber 1. Thus, like the present embodiment, in order for the receivingside to demultiplex SRSs with high accuracy in a case of 2-antenna porttransmission, for example, the difference in the applied cyclic shiftamount between the antenna port with identification number 0 and theantenna port with identification number 1 is 3 or 5 which has the nexthighest demultiplexing performance after 4. This makes it possible toprevent the demultiplexing accuracy from decreasing and also improve theflexibility of SRS resource allocation.

Embodiment 6

Embodiment 6 relates to a variation in the “code resource setting ruletable.”

FIG. 17 is a diagram illustrating a code resource setting rule tableaccording to Embodiment 6 of the present invention.

In FIG. 17 , while basic offset pattern “0, 4, 2, 6” is applied tocyclic shift amount candidates 0 to 3 of an antenna port withidentification number 0, an offset pattern different from the basicoffset pattern is applied to cyclic shift amount candidates 4 to 7 ofthe antenna port with identification number 0. That is, in generalizedexpression, different offset patterns are applied to cyclic shift amountcandidate X and cyclic shift amount candidate X+4 of the antenna portwith identification number 0. In particular, while the basic offsetpattern is applied to cyclic shift amount candidate X, offset pattern“0, 2, A, B” or “0, 6, A, B” is applied to cyclic shift amount candidateX+4. Here, A and B are natural numbers other than 0 and 2 among 0 to 7in a case of offset pattern “0, 2, A, B” and natural numbers other than0 and 6 among 0 to 7 in a case of offset pattern “0, 6, A, B.”

Here, in Embodiment 5, 3 or 5 is added as the difference value betweenthe cyclic shift amount applied to the antenna port with identificationnumber 0 and the cyclic shift amount applied to the antenna port withidentification number 1 to improve the flexibility of SRS resourceallocation while maintaining high SRS demultiplexing performance.However, when the difference value between the cyclic shift amountapplied to the antenna port with identification number 0 and the cyclicshift amount applied to the antenna port with identification number 1 isassumed to be 3 or 5, if this is combined with cyclic shift amount set“0, 4, 2, 6,” there may be cases where SRS resource allocation becomesmore complicated. For example, when terminal 200 to which cyclic shiftamount set “0, 4, 2, 6” is allocated ends SRS transmission at 4 antennaports, resources of cyclic shift amount set “0, 4, 2, 6” become vacant,but SRS resources may be unable to be allocated depending on a cyclicshift amount set in which the difference value between the cyclic shiftamount applied to the antenna port with identification number 0 and thecyclic shift amount applied to the antenna port with identificationnumber 1 is 3 or 5. Thus, when emphasis is placed on the flexibility ofSRS resource allocation as in the case of the present embodiment, 2 or 6is preferably added as the difference value between the cyclic shiftamount applied to the antenna port with identification number 0 and thecyclic shift amount applied to the antenna port with identificationnumber 1.

Applying the basic offset pattern to cyclic shift amount candidate X andapplying offset pattern “0, 2, 4, 6” to cyclic shift amount candidateX+4 makes it possible to secure the flexibility of SRS resourceallocation in 2-transmitting-antenna port transmission which has a highprobability of occurrence, and also maximize a CS interval betweenantenna ports in 4-transmitting-antenna port transmission which has arelatively low probability of occurrence, and thereby maximize the SRSdemultiplexing accuracy.

Embodiment 7

Embodiment 7 relates to a variation in the “code resource setting ruletable.”

FIG. 18 is a diagram illustrating a code resource setting rule tableaccording to Embodiment 7 of the present invention.

In FIG. 18 , different offset patterns are applied to cyclic shiftamount candidate X and cyclic shift amount candidate X+4 of an antennaport with identification number 0. Furthermore, different offsetpatterns are applied to a cyclic shift amount candidate group in whichthe cyclic shift amount of the antenna port with identification number 0is an even number (that is, 0, 2, 4, 6). Basic offset pattern “0, 4, 2,6” is applied to one cyclic shift amount candidate of the cyclic shiftamount candidate group in which the cyclic shift amount of the antennaport with identification number 0 is an even number. In FIG. 18 ,particularly, basic offset pattern “0, 4, 2, 6” is associated withcyclic shift amount candidate 0 of the antenna port with identificationnumber 0. Offset pattern “0, 1, 2, 3” is associated with cyclic shiftamount candidate 2 of the antenna port with identification number 0,offset pattern “0, 2, 4, 6” is associated with cyclic shift amountcandidate 4 of the antenna port with identification number 0, and offsetpattern “0, -1, -2, -3” is associated with cyclic shift amount candidate6 of the antenna port with identification number 0.

Here, in the conventional correspondence table shown in FIG. 2 , when2-antenna port transmission is assumed, the pair of the cyclic shiftamount associated with the antenna port with identification number 0 andthe cyclic shift amount associated with the antenna port withidentification number 1 varies depending on whether the cyclic shiftamount candidate is X or X+2 of the antenna port with identificationnumber 0. However, when only 4-antenna port transmission is assumed, thecyclic shift amount candidate group whose cyclic shift amount is an evennumber (that is, 0, 2, 4, 6) of the antenna port with identificationnumber 0 has the same cyclic shift amount that constitutes the cyclicshift amount set (refer to FIG. 19 ).

In contrast, the present embodiment associates cyclic shift amountcandidate X and cyclic shift amount candidate X+4 of the antenna portwith identification number 0 with different offset patterns, and alsoassociates the cyclic shift amount candidate group whose cyclic shiftamount is an even number (that is, 0, 2, 4, 6) of the antenna port withidentification number 0 with different offset patterns. This makes itpossible to improve the flexibility of SRS resource allocation withoutincreasing the amount of signaling for notification of a cyclic shiftamount.

Embodiment 8

Unlike Embodiments 1 to 7, Embodiment 8 intends to improve theflexibility of SRS resource allocation within a frequency domain. Sincea base station and a terminal of Embodiment 8 have basic configurationscommon to those of base station 100 and terminal 200 of Embodiment 1,their configurations will be described with reference to FIGS. 5 and 6 .

Setting section 101 of base station 100 in Embodiment 8 generates“candidate resource setting information” for setting “candidateresources” of setting target terminal 200. The candidate resourcesetting information can be divided into “time resource settinginformation” and “code frequency resource setting information.”

Reception processing section 108 specifies a resource to which an SRS ismapped based on the setting information and the trigger informationreceived from setting section 101.

To be more specific, reception processing section 108 specifies a timeresource to which the SRS is mapped based on the “time resource settinginformation” and the trigger information. Furthermore, receptionprocessing section 108 specifies a code frequency resource (that is,cyclic shift amount and frequency of a cyclic shift sequence used totransmit the SRS) to which the SRS is mapped based on the “codefrequency resource setting information” and the “code frequency resourcesetting rule table.”

Reception processing section 108 generates a plurality of cyclic shiftsequences (that is, cyclic shift sequence set) corresponding to theplurality of respective specified cyclic shift amounts. Receptionprocessing section 108 then extracts a signal component mapped to thespecified time/frequency resource from the received signal anddemultiplexes a plurality of code-multiplexed SRSs using the generatedcyclic shift sequence set.

In terminal 200 of Embodiment 8, transmission control section 206 sets acandidate resource to which its own terminal maps an SRS.

To be more specific, transmission control section 206 specifies acandidate time resource based on setting information (time resourcesetting information) received from reception processing section 203.

Furthermore, transmission control section 206 specifies a candidate codefrequency resource (that is, cyclic shift amount and frequency of acyclic shift sequence used to transmit an SRS) based on the settinginformation (code frequency resource setting information) received fromreception processing section 203 and the “code frequency resourcesetting rule table.” When the trigger information is received fromreception processing section 203, transmission control section 206outputs information relating to a cyclic shift amount of a cyclic shiftsequence used to transmit an SRS and the frequency to transmissionsignal forming section 207. The candidate frequency resource set in thisterminal 200 will be described in detail later.

Transmission signal forming section 207 maps the SRS received fromreference signal generation section 204 to an RS mapping resourceindicated by RS mapping information. Transmission signal forming section207 then applies a cyclic shift corresponding to information relating tothe cyclic shift amount received from transmission control section 206to a reference sequence, thereby generates a cyclic shift sequence setand multiplies the SRS mapped to the RS mapping resource by the cyclicshift sequence set. The SRSs multiplied by the plurality of respectivecyclic shift sequences that constitute the cyclic shift sequence set aretransmitted from the corresponding antenna ports. The plurality of SRSsare thereby code-multiplexed.

Operations of base station 100 and terminal 200 of Embodiment 8configured as described above will be described. In particular, asetting process for candidate code resources and candidate frequencyresources on setting target terminal 200, an SRS transmission processusing candidate code resources and candidate frequency resources byterminal 200 and a reception process for an SRS transmitted fromterminal 200 by base station 100 will be described here. Furthermore, acase will be described where terminal 200 transmits SRSs using twoantenna ports or four antenna ports.

Setting Process for Candidate Code Resources on Setting Target Terminal200

Setting section 101 generates candidate code frequency resource settinginformation to set candidate code resources and candidate frequencyresources for setting target terminal 200. To be more specific, settingsection 101 generates information relating to the shift amount of acyclic shift sequence used for SRSs transmitted from the referenceantenna port of setting target terminal 200. Here, particularly, thecyclic shift amount regarding an antenna port whose antenna portidentification information is zero is used as information relating tothe cyclic shift amount.

The candidate code frequency resource setting information generated inthis way is transmitted to terminal 200.

SRS Transmission Process Using Candidate Code Frequency Resources ByTerminal 200

Transmission control section 206 sets candidate code frequency resourcesto which its own terminal maps SRSs. To be more specific, transmissioncontrol section 206 specifies candidate code frequency resources (thatis, cyclic shift amount and frequency of the cyclic shift sequence usedto transmit SRSs) based on the code frequency resource settinginformation received from reception processing section 203 and the codefrequency resource setting rule table.

FIG. 20 is a diagram illustrating a code frequency resource setting ruletable according to Embodiment 8 of the present invention. In the codefrequency resource setting rule table, for each of a plurality of cyclicshift amount candidates of a reference antenna port, four antenna portidentification numbers are associated with cyclic shift amounts andfrequencies corresponding to the respective antenna port identificationnumbers. The number of cyclic shift amount candidates is 8 from 0 to 7.In FIG. 20 , in the code frequency resource setting rule table, a fixedoffset pattern “0, 4, 2, 6” is applied to all cyclic shift amountcandidates 0 to 7 of the antenna port with identification number 0.Furthermore, in FIG. 20 , for cyclic shift amount candidates 0 to 3 ofthe antenna port with identification number 0, one frequency band(frequency 1 in FIG. 20 ) is associated with all antenna ports, whereasfor cyclic shift amount candidates 4 to 7 of the antenna port withidentification number 0, one frequency band (frequency 1 in FIG. 20 ) isassociated with the antenna ports with identification number 0 andidentification number 1, and one frequency band (frequency 2 in FIG. 20) is associated with the antenna ports with identification number 2 andidentification number 3. That is, in generalized expression, differentfrequency patterns are applied to cyclic shift amount candidate X andcyclic shift amount candidate X+4 of the antenna port withidentification number 0. Here, X is an integer from 0 to 3 inclusive.

FIG. 21 is a diagram illustrating another example of the code frequencyresource setting rule table according to Embodiment 8 of the presentinvention. In FIG. 21 , for cyclic shift amount candidates 0 to 3 of theantenna port with identification number 0, one frequency band (frequency1 in FIG. 21 ) is associated with all antenna ports. On the other hand,for cyclic shift amount candidates 4 to 7 of the antenna port withidentification number 0, one frequency band (frequency 1 in FIG. 21 ) isassociated with the antenna ports with identification number 0 andidentification number 2, and one frequency band (frequency 2 in FIG. 21) is associated with the antenna ports with identification number 1 andidentification number 3. Above-described frequency 1 and frequency 2 maybe a subcarrier block made up of continuous subcarrier groups or asubcarrier group made up of discretely arranged subcarrier groups (forexample, Comb in LTE). To be more specific, frequency 1 may besubstituted by Comb#0 and frequency 2 may be substituted by Comb#1. Thatis, cyclic shift amount candidates 0 to 3 of the antenna port withidentification number 0 may use only one Comb and cyclic shift amountcandidates 4 to 7 of the antenna port with identification number 0 mayuse only a plurality of Combs. The fixed offset pattern “0, 4, 2, 6” mayhave a different sequence such as “0, 2, 4, 6.” Furthermore, instead ofusing tables such as those shown in FIG. 20 and FIG. 21 , for example,equations may also be used as long as similar processes can beperformed. For example, the following equation may be used instead ofthe figures.

FIG. 20 may also be expressed by equation 1.

$\begin{array}{l}{n_{SRS}^{Comb,\widetilde{p}} = \left( {n_{SRS}^{Comb} + x} \right){mod}2,\,\,\,\,\,\widetilde{p} \in \left\{ {0,...,N_{p} - 1} \right\}} \\{x = \left\{ \begin{array}{l}0 \\\left\lfloor \frac{\widetilde{p}}{2} \right\rfloor\end{array} \right)\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, for\,\,\,\,\,\,\,\,\, n_{SRS}^{CS} = 0 \sim 3} \\{\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, for\,\,\,\,\,\,\, n_{SRS}^{CS} = 4 \sim 7\,}\end{array}$

n_(SRS)^(Comb, p̃)

is information indicating SRS arrangement of an antenna port withidentification number p̃ (for example, frequency 1 and frequency 2 orComb#0 and Comb#1).

n_(SRS)^(CS)

and

n_(SRS)^(Comb)

are information indicating a cyclic shift amount and SRS arrangement ofan antenna port with identification number 0 notified of by the basestation.

⌊A⌋

is a maximum integer smaller than A. Frequency 1 (or Comb#0) when

n_(SRS)^(Comb, p̃)

is 0, or frequency 2 (or Comb#1) when

n_(SRS)^(Comb, p̃)

is 1 is applied at the terminal station and the base station.

n_(SRS)^(Comb)

may be a value (0 or 1) explicitly notified of by the base station ormay be implicitly notified of or a fixed value.

n_(SRS)^(CS)

need not be limited to the classification such as 0 to 3 and 4 to 7 andmay be changed based on Embodiments 1 to 7 or the like. N_(p) is thenumber of antenna ports used for SRS transmission.

Similarly, FIG. 21 can also be expressed by equation 2.

$\begin{array}{l}{n_{SRS}^{Comb,\widetilde{p}} = \left( {n_{SRS}^{Comb} + x} \right){mod}2,\,\,\,\,\,\widetilde{p} \in \left\{ {0,...,N_{p} - 1} \right\}} \\{x = \left\{ \begin{array}{l}0 \\\widetilde{p}\end{array} \right)\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, for\,\,\,\,\,\,\,\,\, n_{SRS}^{CS} = 0 \sim 3} \\{\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, for\,\,\,\,\,\,\, n_{SRS}^{CS} = 4 \sim 7\,}\end{array}$

Furthermore, when FIG. 21 and FIG. 20 are used assuming that the numbersof antenna ports is 2 and 4 respectively, equation 3 is obtained.

$\begin{array}{l}{n_{SRS}^{Comb,\widetilde{p}} = \left( {n_{SRS}^{Comb} + x} \right){mod}2,\,\,\,\,\,\widetilde{p} \in \left\{ {0,...,N_{p} - 1} \right\}} \\{x = \left\{ \begin{array}{l}0 \\\left\lfloor \frac{2\widetilde{p}}{N_{p}} \right\rfloor\end{array} \right)\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, for\,\,\,\,\,\,\,\,\, n_{SRS}^{CS} = 0 \sim 3} \\{\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, for\,\,\,\,\,\,\, n_{SRS}^{CS} = 4 \sim 7\,}\end{array}$

Here, in Embodiments 1 to 7, different offset patterns are associatedwith cyclic shift amount candidate X and cyclic shift amount candidateX+4 of the antenna port with identification number 0. However, themethod for improving the flexibility of SRS resource allocation is notlimited to this. That is, as described above, the flexibility of SRSresource allocation can also be improved by associating cyclic shiftamount candidate X and cyclic shift amount candidate X+4 of the antennaport with identification number 0 with different frequency patterns.

Frequency 1 and frequency 2 may also be considered as amounts of offsetin the frequency domain. For example, when base station 100 notifies ofinformation indicating Comb#0 and cyclic shift amount candidate 0 of theantenna port with identification number 0, terminal 200 transmits an SRSusing only Comb#0, whereas when base station 100 notifies of informationindicating Comb#1 and cyclic shift amount 0 of the antenna port withidentification number 0, terminal 200 transmits an SRS using onlyComb#1.

Other Embodiments

(1) In the above each embodiment, some of the plurality of cyclic shiftamount candidates of the reference antenna port may be associated withtrigger information (that is, trigger bits in PDCCH). For example, usingsetting information, cyclic shift amount candidate 0 of the referenceantenna port is associated with trigger information 1 of PDCCH, andcyclic shift amount candidate 4 of the reference antenna port isassociated with trigger information 2 of PDCCH. When base station 100notifies terminal 200 of trigger information 1 of PDCCH, terminal 200transmits an SRS using a cyclic shift amount set with which cyclic shiftamount candidate 0 of the reference antenna port is associated, and whenbase station 100 notifies terminal 200 of trigger information 2 ofPDCCH, terminal 200 transmits an SRS using a cyclic shift amount setwith which cyclic shift amount candidate 4 of the reference antenna portis associated.

(2) The table described in the above each embodiment is applicable toone of a case of only 2-antenna port transmission, a case of only4-antenna port transmission, and a case of both 2-antenna porttransmission and 4-antenna port transmission. Furthermore, differenttables may be used for a case of 4-antenna port transmission and for acase of 2-antenna port transmission.

(3) The above each embodiment has been described assuming that the samecyclic shift amount of the antenna port with identification number 0 isused when one antenna port is used, and when two or four antenna portsare used. However, the present invention is not limited to this, and thecorrespondence between the antenna port with identification number 0 andthe cyclic shift amount may differ when one antenna port is used, andwhen two or four antenna ports are used.

(4) The above each embodiment has described SRSs (for example, DA-SRS,P-SRS), but the present invention is not limited to this, and anyreference signal may be applicable as long as it can be code-multiplexedwith a cyclic shift sequence.

(5) The antenna port in the above each embodiment represents a logicalantenna (antenna group) formed by one or a plurality of physicalantennas. In other words, the antenna port is not limited to representone physical antenna, and may include an array antenna formed by aplurality of antennas, for example. For example, the number of physicalantennas for forming the antenna port is not defined, and the antennaport is defined as a minimum unit by which a terminal can transmitreference signals. The antenna port may also be defined as a minimumunit for multiplying weighting of a precoding vector.

(6) A case has been described in the above each embodiment where thenumber of notification bits is 3 and cyclic shift amount candidates are0 to 7 as a premise, but the present invention is not limited to this.For example, the number of notification bits may be 4 and cyclic shiftamount candidates may be 0 to 15. In this case, offset amount set “0, 4,2, 6” may be an M (M=2 in a case of 4 bits) multiple of the offsetamount such as “0, 8, 4, 12.” Furthermore, the cyclic shift amounts ofthe antenna ports with identification numbers 1 to 3 are not limited tothe values in the figures, either. For example, the cyclic shift amountsmay be offset amount set “0, 2, 4, 6.”

(7) Although the above each embodiment has been described using a casewhere the present invention is implemented with hardware, as an example,the present invention can be implemented with software in interworkingwith hardware.

Furthermore, each function block employed in the explanation of theabove each embodiment may typically be implemented as an LSI constitutedby an integrated circuit. These function blocks may be individual chipsor partially or totally contained on a single chip. The term “LSI” isadopted herein but this may also be referred to as “IC,” “system LSI,”“super LSI,” or “ultra LSI,” depending on the differing extents ofintegration.

The method of implementing integrated circuit is not limited to LSI, andimplementation by means of dedicated circuitry or a general-purposeprocessor may also be possible. After LSI manufacture, utilization of afield programmable gate array (FPGA) or a reconfigurable processor whereconnections and settings of circuit cells in an LSI can be reconfiguredis also possible.

If a new integrated circuit implementation technology replacing LSI isintroduced because of advancement in semiconductor technology or adifferent technology derived therefrom, the function blocks may ofcourse be integrated using that technology. For example, application ofbiotechnology is possible.

The disclosure of Japanese Patent Application No. 2011-001829, filed onJan. 7, 2011 and Japanese Patent Application No.2011-009870, filed onJan. 20, 2011, including the specification, drawings and abstract, isincorporated herein by reference in their entirety.

Industrial Applicability

The transmitter apparatus, receiver apparatus, transmission method, andreception method of the present invention are useful to improve theflexibility of SRS resource allocation without increasing the amount ofsignaling for notification of a cyclic shift amount.

Reference Signs List 100 base station 101 setting section 102, 103coding/modulation section 104 transmission processing section 105, 208transmitting section 106, 201 antenna 107, 202 receiving section 108,203 reception processing section 109 data receiving section 110receiving quality measuring section 200 terminal 204 reference signalgeneration section 205 data signal generation section 206 transmissioncontrol section 207 transmission signal forming section

1. A communication apparatus, comprising: circuitry, which in operation,maps reference signals of a first antenna port and a second antenna portto frequency resources determined from a plurality of candidates,wherein the plurality of candidates include a first candidate and asecond candidate, the first candidate includes only first frequencyresources, and the second candidate includes the first frequencyresources and second frequency resources which are different from thefirst frequency resources; and a transmitter, which in operation,transmits the reference signals of the first antenna port and the secondantenna port on the determined frequency resources, wherein, in thefirst candidate the first frequency resources are used for the referencesignals of the first antenna port and the second antenna port, and inthe second candidate the first frequency resources are used for thereference signals of the first antenna port and the second frequencyresources are used for the reference signals of the second antenna port,wherein information indicating one of the plurality of candidates, whichincludes the first candidate and the second candidate, is transmittedvia a physical downlink control channel (PDCCH), and wherein the firstfrequency resources include a first subcarrier and a third subcarrier,the second frequency resources include a second subcarrier and a fourthsubcarrier, the second subcarrier is allocated between the firstsubcarrier and the third subcarrier, and the third subcarrier isallocated between the second subcarrier and the fourth subcarrier. 2.The communication apparatus according to claim 1, wherein the referencesignals of the first antenna port and the second antenna port aremultiplexed by orthogonal sequences on the first frequency resources inthe first candidate, and the reference signals of the first antenna portare multiplexed by orthogonal sequences on the first frequency resourcesand the reference signals of the second antenna port are multiplexed byorthogonal sequences on the second frequency resources in the secondcandidate.
 3. The communication apparatus according to claim 1, wherein,when a cyclic shift index of the first antenna port is less than orequal to a determined number, the reference signals of the first antennaport and the second antenna port are mapped to the first frequencyresources.
 4. The communication apparatus according to claim 1, wherein,when a cyclic shift index of the first antenna port is less than orequal to a determined number, the first frequency resources correspondto all index numbers of a plurality of antenna ports.
 5. Thecommunication apparatus according to claim 1, wherein, when a cyclicshift index of the first antenna port is greater than a determinednumber, the first frequency resources correspond to odd index numbers ofa plurality of antenna ports and the second frequency resourcescorrespond to even index numbers of the plurality of antenna ports. 6.The communication apparatus according to claim 1, wherein a number of aplurality of antenna ports is four, the first frequency resourcescorrespond to antenna ports with index numbers 1 and 3, and the secondfrequency resources correspond to antenna ports with index numbers 2 and4 when a cyclic shift index of the first antenna port is greater than adetermined number.
 7. The communication apparatus according to claim 1,wherein each of the second frequency resources is adjacent to arespective one of the first frequency resources.
 8. A communicationmethod comprising: mapping reference signals of a first antenna port anda second antenna port to frequency resources determined from a pluralityof candidates, wherein the plurality of candidates include a firstcandidate and a second candidate, the first candidate includes onlyfirst frequency resources, and the second candidate includes the firstfrequency resources and second frequency resources which are differentfrom the first frequency resources; and transmitting the referencesignals of the first antenna port and the second antenna port on thedetermined frequency resources, wherein, in the first candidate thefirst frequency resources are used for the reference signals of thefirst antenna port and the second antenna port, and in the secondcandidate the first frequency resources are used for the referencesignals of the first antenna port and the second frequency resources areused for the reference signals of the second antenna port, whereininformation indicating one of the plurality of candidates, whichincludes the first candidate and the second candidate, is transmittedvia a physical downlink control channel (PDCCH), and wherein the firstfrequency resources include a first subcarrier and a third subcarrier,the second frequency resources include a second subcarrier and a fourthsubcarrier, the second subcarrier is allocated between the firstsubcarrier and the third subcarrier, and the third subcarrier isallocated between the second subcarrier and the fourth subcarrier. 9.The communication method according to claim 8, wherein the referencesignals of the first antenna port and the second antenna port aremultiplexed by orthogonal sequences on the first frequency resources inthe first candidate, and the reference signals of the first antenna portare multiplexed by orthogonal sequences on the first frequency resourcesand the reference signals of the second antenna port are multiplexed byorthogonal sequences on the second frequency resources in the secondcandidate.
 10. The communication method according to claim 8, wherein,when a cyclic shift index of the first antenna port is less than orequal to a determined number, the reference signals of the first antennaport and the second antenna port are mapped to the first frequencyresources.
 11. The communication method according to claim 8, wherein,when a cyclic shift index of the first antenna port is less than orequal to a determined number, the first frequency resources correspondto all index numbers of a plurality of antenna ports.
 12. Thecommunication method according to claim 8, wherein, when a cyclic shiftindex of the first antenna port is greater than a determined number, thefirst frequency resources correspond to odd index numbers of a pluralityof antenna ports and the second frequency resources correspond to evenindex numbers of the plurality of antenna ports.
 13. The communicationmethod according to claim 8, wherein a number of a plurality of antennaports is four, the first frequency resources correspond to antenna portswith index numbers 1 and 3, and the second frequency resourcescorrespond to antenna ports with index numbers 2 and 4 when a cyclicshift index of the first antenna port is greater than a determinednumber.
 14. The communication method according to claim 8, wherein eachof the second frequency resources is adjacent to a respective one of thefirst frequency resources.